Resist sensitivity, improvement halogenation

It is formed by acylases that cleave off the side chain of the penicillins, and can also be obtained by the selective chemical cleavage of the amide, leaving the lactam intact. After this, 6-APA can be easily acylated by any carboxylic acid, and this has yielded literally thousands of semisynthetic penicillins in the past 30 years, many showing improved stability and activity. Some of them are lactamase resistant (methicillin (9.41), oxacillin (9.42) and its halogenated derivatives), whereas others are broad-spectrum antibiotics, like the orally active ampicillin (9.43), which also inhibits Gramnegative bacteria but is sensitive to lactamase. Carbenicillin (9.44) is particularly active against Pseudomonas and Proteus infections, which are unaffected by natural penicillins. Piperacillin (9.45), a broad-spectrum compound, is spectacularly active against Pseudomonas. 

We note from Table VIII a strong interest in halogenated resists, particularly those substituted with chlorine. The addition of chlorine to the aromatic structure of polystyrene has a marked effect on cross-linking efficiency. Monodisperse polystyrene, for example, has a sensitivity on the order of 50 p C/cm2, yet with as little as 20% chloromethyl groups substituted on the ring, the sensitivity is improved to 2 C/cm2 for comparable molecular weight and distribution. 

Resists based on chloromethyl substitution have been extensively studied in the past few years (7-7). Halogen and halomethyl groups have been introduced by a variety of methods. Choong and Kahn (7) synthesized polychloromethylstyrene (PCMS) by free radical polymerization of chloromethylstyrene and reported a sensitivity (D 5) of 0.4 / 2 at 20 kV with a contrast of 1.5 for materials with molecular weight of about 400,000 (7). The molecular weight distribution of these polymers, all of which contained one chloromethyl group per repeat unit, was about 2. Fractionation of the polymer resulted in improved contrast as a result of narrowing the distribution. 

Alkali and acid treatments have also been used to modify surface properties of polymers sulfonated polyethylene films treated first with ethylenediamine and then with a terpolymer of vinyhdene chloride, acrylonitrile, and acrylic acid exhibited better clarity and scuff resistance and reduced permeabihty. Permanently amber-colored polyethylene containers suitable for storing light-sensitive compoimds have been produced by treating fluorosulfonated polyethylene with alkali. Poly(ethylene terephthalate) dipped into trichloroacetic/chromic acid mixture has improved adhesion to polyethylene and nylons. Antifogging lenses have been prepared by exposing polystyrene films to sulfonating conditions. Acid and alkali surface treatments have also been used to produce desired properties in polymethylmethacrylates, polyacrylonitrile, styrene-butadiene resins, polyisobutylene, and natural rubber. Surface halogenation of the diene polymers natural rubber and polyisobutylene resulted in increased adhesion to polar surfaces. 

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